1. Field of the Invention
The invention relates to a damping arrangement for reducing resonant vibrations in a combustion chamber, with a combustion-chamber wall which is of double-walled design, and, with an outer wall-surface part and an inner wall-surface part facing the combustion chamber, gastightly encloses an intermediate space, into which cooling air can be fed for purposes of convective cooling of the combustion-chamber wall.
2. Discussion of Background
A combustion chamber with a combustion-chamber wall of double-walled design mentioned above emerges from EP 0 669 500 B1. There is a flow of compressed combustion feed air for cooling purposes through the enclosed intermediate space of the combustion-chamber wall of double-walled design which surrounds the combustion zone, the combustion-chamber wall of double-walled design being cooled by way of convective cooling. Further details of the particular configuration of a combustion chamber of this kind can be found in the abovementioned European patent, to the disclosure of which explicit reference is made at this point.
Combustion chambers constructed in this way are used primarily for the operation of gas turbines but are also used generally in heat-generating systems, e.g. for firing boilers.
Under certain operating conditions, noise in the form of thermal acoustic vibrations occurs in these combustion chambers and may well show highly pronounced resonant phenomena in the frequency range between 20 and 400 Hz. Such vibrations, which are also known as combustion-chamber pulsations, can assume amplitudes and associated pressure fluctuations that subject the combustion chamber itself to severe mechanical loads that may decisively reduce the life of the combustion chamber and, in the worst case, may even lead to destruction of the combustion chamber.
Since the formation of such combustion-chamber pulsations depends on a large number of boundary conditions, it is difficult or impossible to predetermine precisely the occurrence of such pulsations. On the contrary, it is necessary to respond appropriately during the operation of the combustion chamber in cases of resonant vibration increases, by deliberately avoiding combustion-chamber operating points at which high pulsation amplitudes occur, for example. However, it is not always possible to implement such a measure, especially since, when starting up a gas turbine system, for example, a large number of particular operating states have to be traversed in order to be able to reach the corresponding optimum rated operating range for the gas turbine.
On the other hand, measures for the selective damping of resonant combustion-chamber pulsations of this kind by means of devices, e.g. using suitable acoustic damping elements such as Helmholtz dampers or λ/4 tubes, are known. Acoustic damping elements of this kind generally comprise a bottleneck and a larger volume connected to the bottleneck, which is matched in each case to the frequency to be damped. Especially when selectively damping low frequencies, there is a need for large damping volumes, which cannot be integrated into every combustion chamber for design reasons.
Active countermeasures are also known for selectively combating combustion-chamber pulsations, by means of which anti-sound fields, for example, are coupled into the combustion chamber for the selective suppression or elimination of resonant pressure fluctuations.
All the initially mentioned measures for selectively damping combustion-chamber pulsations are matched individually to the corresponding conditions of the individual combustion chambers and cannot readily be applied to other types of combustion chamber.
The combustion chamber described at the outset with convective cooling within the combustion-chamber wall, which is of double-walled design, has been optimized in light of combustion with low pollutant emissions. With a combustion chamber of this kind, it is furthermore possible to achieve very lean combustion using a relatively high proportion of air.